In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (2G) and/or user equipments (UE), communicate via a Radio access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, with each service area or cell area being served by radio network node such as an access node e.g. a Wi-Fi access point or a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” or “eNodeB”. The service area or cell area is a geographical area where radio coverage is provided by the access node. The access node operates on radio frequencies to communicate over an air interface with the wireless devices within range of the access node. The access node communicates over a downlink (DL) to the wireless device and the wireless device communicates over an uplink (UL) to the access node.
A Universal Mobile Telecommunications System (UMTS) is a third generation telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High-Speed Packet Access (HSPA) for communication with user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for present and future generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several access nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural access nodes connected thereto. The RNCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS) have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, such as 4G and 5G networks. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long-Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a 3GPP radio access technology wherein the access nodes are directly connected to the EPC core network. As such, the Radio Access Network (RAN) of an EPS has an essentially “flat” architecture comprising access nodes connected directly to one or more core networks.
With the emerging 5G technologies, the use of very many transmit- and receive-antenna elements is of great interest as it makes it possible to utilize beamforming, such as transmit-side and receive-side beamforming. Transmit-side beamforming means that a transmitter can amplify the transmitted signals in a selected direction or directions, while suppressing the transmitted signals in other directions. Similarly, on the receive-side, a receiver can amplify signals from a selected direction or directions, while suppressing unwanted signals from other directions.
Beamforming allows the signal to be stronger for an individual connection. On the transmit-side this may be achieved by a concentration of the transmitted power in the desired direction(s), and on the receive-side this may be achieved by an increased receiver sensitivity in the desired direction(s). This beamforming enhances throughput and coverage of the connection. It also allows reducing the interference from unwanted signals, thereby enabling several simultaneous transmissions over multiple individual connections using the same resources in the time-frequency grid, so-called multi-user Multiple Input Multiple Output (MIMO).
Overall requirements for the Next Generation (NG) architecture e.g. TR 23.799 v.0.5.0, and, more specifically the NG Access Technology, e.g. TR 38.913 v.0.3.0 will impact the design of the Active Mode Mobility solutions for the New Radio Access Technology (NR), see RP-160671 New SID Proposal: Study on New Radio Access Technology, DoCoMo, compared to the current mobility solution in LTE. Some of these requirements are the need to support network energy efficiency mechanisms, future-proof-ness and the need to support a very wide range of frequencies e.g. up to 100 GHz.
One of the main differences, with respect to LTE, comes from the fact that propagation in frequencies above the ones allocated to LTE is more challenging so that the massive usage of beamforming becomes an essential component of NR. Despite the link budget gains provided by beamforming solutions, reliability of a system purely relying on beamforming and operating in higher frequencies might be challenging, since the coverage might be more sensitive to both time and space variations. As a consequence of that a Signal to Interference plus Noise Ratio (SINR) of a narrow link can drop much quicker than in the case of LTE, see R2-162762, Active Mode Mobility in NR: SINR drops in higher frequencies, Ericsson.
To support Transmit (Tx)-side beamforming at a radio network node, a number of reference signals (RS) may be transmitted from the radio network node, whereby the wireless device can measure signal strength or quality of these reference signals and report the measurement results to the radio network node. The radio network node may then use these measurements to decide which beam(s) to use for the one or more wireless devices.
A combination of periodic and scheduled reference signals may be used for this purpose.
The periodic reference signals, typically called beam reference signals (BRS) or Mobility Reference Signals (MRS), are transmitted repeatedly, in time, in a large number of different directions using as many Tx-beams as deemed necessary to cover a service area of the radio network node. As the naming indicates, each BRS represents a unique Tx-beam from that radio network node. This allows a wireless device to measure the BRS when transmitted in different beams, without any special arrangement for that wireless device from the radio network node perspective. The wireless device reports e.g. the received powers for different BRSs, or equivalently different Tx-beams, back to the radio network node.
The scheduled reference signals, called channel-state information reference signals (CSI-RS), are transmitted only when needed for a particular connection. The decision when and how to transmit the CSI-RS is made by the radio network node and the decision is signalled to the involved wireless devices using a so-called measurement grant. When the wireless device receives a measurement grant it measures on a corresponding CSI-RS. The radio network node may choose to transmit CSI-RSs to a wireless device only using beam(s) that are known to be strong for that wireless device, to allow the wireless device to report more detailed information about those beams. Alternatively, the radio network node may choose to transmit CSI-RSs also using beam(s) that are not known to be strong for that wireless device, for instance to enable fast detection of new beam(s) in case the wireless device is moving.
The radio network nodes of e.g. an NR network transmit other reference signals as well. For instance, the radio network nodes may transmit so-called demodulation reference signals (DMRS) when transmitting control information or data to a wireless device. Such transmissions are typically made using beam(s) that are known to be strong for that wireless device.
Beamforming introduces a possibility to enhance the signal towards a specific location. This enables better signal to noise ratio towards a specific wireless device.
A specific beamforming towards a specific wireless device is handled per Transmission Time Interval (TTI) where a number of factors and measurements are used to determine how the beamforming should look like. With an increasing number of antenna elements, the number of possible beams that theoretically can be created increases a lot.
One key design principle currently under consideration for 5G is to base it on an ultra-lean design. This implies that “always on signals” should be avoided from the network as much as possible. The expected benefit from this design principle is expected to be significantly lower network energy consumption, better scalability, higher degree of forward compatibility during the RAT evolution phase, lower interference from system overhead signals and consequently higher throughput in low load scenario, and improved support for user centric beam-forming.
Advanced antenna systems (AAS) is an area where technology has advanced significantly in recent years and where a rapid technology development is foreseen in the years to come. Hence it is natural to assume that advanced antenna systems in general and massive MIMO transmission and reception in particular will be a cornerstone in a future 5G system.
Beam-formed control information, e.g. enhanced Physical Downlink Control Channel (ePDCCH). Beam-forming becomes increasingly popular and capable and therefore it is natural to use it not only for transmission of data but also for transmission of control information. This is one motivation behind the (relatively) new control channel in LTE known as ePDCCH. When the control channel is beam-formed the cost of transmitting the overhead control information can be reduced due to the increased link budget provided by the additional antenna gain. This is a good property that may be utilized also for 5G, perhaps to an even larger degree than what is possible in the current LTE standard.
Radio network nodes may rely on relations or neighbour relationships, either between radio network nodes or between different sectors, controlled by the same or different radio network nodes, or a combination. The neighbour relationships can be only in one direction or mutual. Mechanisms to establish neighbour relationships vary in different wireless communication networks.
The neighbour relationships are illustrated by FIG. 1, where a radio network node can have an isolated or distributed architecture and logical functions are mapped to the architecture. A resource control function (RCF) maintains higher layer aspects of radio connections, while lower layer aspects are handled by a baseband processing function (BPF). FIG. 1 illustrates without loss of generality two RCFs, RCF1, controlling (7) BPF11 and (2) BPF12, and RCF2, controlling (3) BPF21. A BPF can serve one or more transceivers
Network node neighbour relationships comprises:                Relationships between RCFs denoted 5 in FIG. 1        Relationships between BPFs denoted 4 in FIG. 1        Relationships between transceivers denoted 6 in FIG. 1        
Beams are associated to reference signals, which here are referred to as mobility reference signals, and denoted MRSijk with i relating to the controlled RCF, j relating to the controlling BPF and k a local enumerable of beams within the BPF. This is just an example of labelling. Beams can reach the wireless device directly, e.g. MRS111, or after one or more reflections, e.g. MRS112.
Neighbour Relationships between beams can be between beams controlled by                the same BPF, like MRS111 and MRS112        different BPFs, but the same RCF, like MRS111 and MRS121        different BPFs and RCFs, like MRS111 and MRS211        
A robustness of a radio connection, also referred to as connection or a signal connection, depends on the radio resource management situation associated with the serving radio network node or nodes, as well as the radio conditions associated to alternative radio network nodes. Such radio network nodes may be alternative candidates to serve the wireless device, but may also induce interference to hamper the radio connection. The mechanisms to ensure the robustness of the radio connection depend on the means to interact with the wireless device such as the frequency of radio condition status information, and the frequency of resource control command opportunities. Moreover, such procedures may rely on neighbour relationships, and suffer from absence of neighbour relationships.
When the radio connection robustness fails, it may be due to the absence of a neighbour relationship and that existing mechanisms to establish such a neighbour relationship have failed, which is a problem with existing solutions resulting in a reduced or limited performance of the wireless communication network.